1. Field of the Invention
The present invention relates to drying semiconductor structures. More particularly, the present invention relates to the minimization of water spotting and of oxide growth that are experienced on semiconductor structures during chemical treatment steps, deionized (DI) water rinse steps, and drying steps. Examples of minimization of water spotting and of oxide growth are given for an HF rinse process in which the steps of DI water rinsing and drying are combined.
2. State of the Art
Producing a substantially impurity-free semiconductor structure is an ongoing challenge during fabrication of operable integrated circuits and other microelectronic devices. During fabrication, several operations are completed with a chemical treatment such as a polysilicon etching, a photoresist stripping, an RCA cleaning, or a buffered oxide etching (BOE). Following a chemical treatment, rinsing the structure to remove treatment chemicals is required.
Following a chemical treatment such as an HF rinse cleaning, a semiconductor structure is typically transferred to a vessel for a DI water rinse and then to a dryer to be dried. With each transfer of the semiconductor structure during fabrication between processing vessels, the possibility of contamination increases and, with that, also the likelihood of lower process yield. In chemical treatments of semiconductor structures that result in exposed hydrophobic surfaces, the possibility of oxidation and particle contamination is high.
During an HF-last rinse of a semiconductor structure with exposed silicon, for example, a significant number of (Si)2=O bonds are changed to Sixe2x80x94H bonds. About ten to twenty percent of the changed bonds, however, are Sixe2x80x94F instead of the preferred Sixe2x80x94H. During the industry standard DI water rinse that follows most chemical treatments, the Sixe2x80x94F bonds in this example are easily washed off, and oxidation of semiconductor materials, such as silicon, occurs while transferring the semiconductor structure from a rinsing vessel to a drying vessel. Oxidation can occur both during the transfer to the drying vessel and while the semiconductor structure resides in the drying vessel prior to drying.
Before the semiconductor device is moved to the next fabrication phase, substantially complete drying must be accomplished because any water that remains on the surface of a semiconductor structure has the potential of interfering with subsequent processing. Drying can be accomplished in spin-rinse dryers (SRDs), Marangoni dryers, axial dryers and others used in the art.
Various drying techniques such as spin drying also cause water spotting. During spin drying, water spotting droplet tracks are left on the hydrophobic faces of the semiconductor structures. These water spotting tracks are formed from slight impurities contained in the DI water droplets. Water spotting is caused due to the hydrophobic nature of the cleaned silicon and other surfaces such as metallization lines.
As DI water is spun off from the hydrophobic face of a semiconductor structure, water droplet size decreases. Any portion of the DI water droplet that is not pure water is attracted to the hydrophobic surfaces of the semiconductor structure, while the water portion is repelled. Because the water droplets become exceedingly small, dissolved impurities are more strongly attracted to the hydrophobic surfaces of the semiconductor structure than they are to remaining in solution within the water droplet.
The Marangoni drying technique reduces water spotting that is incident to spin drying. In the Marangoni drying technique, a chemically treated semiconductor structure is DI water rinsed, transferred to the Marangoni dryer, immersed in a DI water bath, and drawn through an isopropyl alcohol (IPA) layer that rests on the surface of the DI water bath. In the Marangoni technique, the forces that attract impurities to exposed hydrophobic semiconductor structure surfaces are balanced by the bulk of the water in the relatively pure DI water bath that tends to keep the impurities in solution. When employing the Marangoni drying technique, the DI water and its impurities are entrained beneath the water-IPA interface while the semiconductor structure is drawn through the interface.
Marangoni drying reduces water spotting, but it does not ameliorate oxidative contamination that occurs upon a semiconductor structure during transfer of the semiconductor structure from the DI water rinsing vessel to the dryer. Thus, elimination of the deleterious effects of water spotting may be overshadowed by contamination of the semiconductor structure experienced simply during transfer from one vessel to another.
Because a Marangoni dryer may have moving parts, the function of which is to draw a wafer boat out of a DI water bath, the possibility of particulate contamination arises, which contamination is caused by abrasion of surfaces on the moving parts.
What is needed is a method of rinsing and drying semiconductor structures, particularly hydrophobic semiconductor structures, in such a way as to substantially eliminate oxide contamination incident to semiconductor structure transfer from vessel to vessel and by water spotting incident to spin drying. What is also needed is a device that will accomplish the inventive method while simplifying the Marangoni technique and equipment.
The present invention relates to a method of cleaning and drying semiconductor structures. The present invention also relates to a method of using a conventional gas etch/rinse vessel, or a conventional dryer vessel. The present invention also relates to an apparatus that accomplishes the inventive method. The present invention reduces the likelihood of oxide contamination and the like, as well as the incidence of water spotting.
In a first embodiment of the present invention, a semiconductor structure is placed into a first treatment vessel for a chemical treatment. Following the chemical treatment, the semiconductor structure is transferred directly from the first treatment vessel to a second treatment vessel. The semiconductor structure is rinsed with DI water in the second treatment vessel. Next, the second treatment vessel is flooded with DI water to form a DI water bath. The second treatment vessel may also be optionally flooded with a gas that is inert to the ambient, such as nitrogen, to form in the second treatment vessel an inert atmosphere. The inert gas forming the inert atmosphere is intended herein to mean a gas that does not substantially react with or otherwise contaminate the semiconductor structure or the vessel in which the inert atmosphere is formed under the processing conditions set forth herein. The inert atmosphere is maintained during rinsing. Following rinsing, a gaseous stream, such as nitrogen, that is laden with IPA vapor is fed into the second treatment vessel.
After a selected period of time, a layer of IPA has formed upon the surface of the DI water bath to form an IPA-DI water interface. The semiconductor structure is drawn out of the DI water bath at a preferred rate that causes substantially all the DI water, and contaminants therein, to be entrained beneath the IPA-DI water interface.
In a second embodiment of the present invention, a dry etch is performed. The process of the second embodiment comprises first placing a semiconductor structure into a gas etch chamber. After placing a semiconductor structure into a gas etch chamber, the gas etch chamber is sealed and gas etching of the semiconductor structure commences. Following gas etching, the semiconductor structure is rinsed with DI water. After rinsing and an optional washing of the semiconductor structure in the gas etch chamber, the gas etch chamber is purged of any gas that is not inert to the semiconductor structure or to the gas etch chamber. The semiconductor structure is then submerged in DI water by flooding the gas etch chamber, wherein a surface of DI water forms above the semiconductor structure. Nitrogen gas laden with IPA vapor is introduced into the gas etch chamber to form an IPA-DI water interface upon the surface of the DI water. Finally, the gas etch chamber is drained by displacing the DI water bath with more IPA-laden nitrogen. As the gas etch chamber is drained at a preferred rate, the IPA-DI water interface functions as a dynamic barrier to the DI water and substantially xe2x80x9cwipes downxe2x80x9d the semiconductor structure by substantially entraining the DI water, and contaminants therein, beneath the IPA.
In a third embodiment of the present invention, a rinser is retrofit with a lid and a fail-shut valve. In the third embodiment, the process of chemical treatment is carried out conventionally, but DI water rinsing and drying both occur within the rinser. Following sufficient rinse cycles, IPA-laden nitrogen is fed into the rinser in a manner similar to the method of the second embodiment. Entrainment of substantially all DI water, and contaminants therein, beneath the IPA layer is accomplished by displacement of the last spray/dump DI water volume with an IPA-DI water interface as set forth above. In this embodiment, retrofit rinsers include spray/dump rinsers, overflow rinsers, cascade rinsers, and Marangoni dryers that have been retrofit with rinsing capabilities.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.